Apparatus for determining oxygen in gases



Feb. 6, 1951 M. a. JACOBSON APPARATUS FOR MINING OXYGEN IN BASES 2Shuts-Shut. 1

Original Filed Kay 22, 1943 mama. flared-G. Jncoasav.

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0 TTORNE Y5 Patented Feb. 6, 1951 UNITED STATES PATENT OFFICE streamAPPARATUS IOl DWI 0x101 I IN oases Moses aeorporan Original applicationIn! W and I G.Iacobaon.Verona,Pa-,assignortol Safety AW Company this1946, Berhl No. if!

8 Claims. (Cl. 115-49) This invention relates to apparatus for thedetermination of the concentration of oxygen in air and other gases.

Although the invention is applicable to the determination of oxygenconcentrations at least as high as 99per cent, it is particularly usefulfor determining the deilciency of oxygen in air atm'ospheres, for whichreason-it will be described with particular reference thereto. I

There has existed a need for a portable oxygen deficiency meter which iseasily used. does not create an explosion or fire hazard in use,

and is sumciently accurate for all practical purposes. Thus, such oxygendeficiency detectors are useful in connection with mine and manholeatmospheres, in high altitude flying, for useln submarines, and forrelated purposes. At present. mine and manhole atmospheres are commonlytested for oxygen deficiency by means of the wellknown flame safetylamp,. which is useful to give a qualitative indication of oxygendeficiency down to 16 per cent of oxygen; below that conline burgh,

I2. 1043, Beta! No. application lanai!- under flyin or 0 ther conditionswhere it may not be practicable to keep the apparatus upright atalltimes. AgainlthasbeenfoundthatinawU-'ingthe'priorsuggestionstemperaturehssalarge centration the name isextinguished. Moreover.

name lamps are not proof against accident in. for example. manholes intowhich city gas containin; hydrogen may escape. For such purposes itwould be desirable to have means available for determining the oxygenconcentration or deficiency accurately, rapidly. and with safety.

Primary cells of the Fery typ comprisins a zincanode, a porous carboncathode, and a solution of ammonium chloride as the electrolyte, dependfor depolarization upon atmospheric oxygen which diiluses through thecathode and acts at the electrode-electrolyte interface to oxidize thehydrogen ions liberated at the cathode. The extent of depolarization isa function of the oxygen reaching the interface, and it has thereforebeen proposed to use such a galvanic cell for determining oxygenconcentration of gases. Particularly. such a system would be desirablefor use under widely varying conditions of barometric pressure becausecell is directly proportional to, the barometric pressure. Thus, a 10.6per cent concentration of oxygen, 160 mm. pressure will cause the samemeter deflection as a 21 per cent concentration at 380 mm. This isdesirable for makingmeasuremcnts at high altitudes or under subsurfaceconditions because (or such purposes the import ant thing is the partialpressure of oxygen rather than its volume concentration.

However, the prior proposals do not afford a satisfactory instrument fordetermining oxygen concentration, and they have not resulted inanyiniluencs upon ti ie meter readings. and it is neces- Bar! tomaintain certain critical relations in the electrical circuit Experiencehas shown also that difficulties are e icountered with the cathodebecause ditferent iarbons. even from the same lot, exhibit difl'erenidegrees of sensitivity which nceessitates recalibration of theinstrument each time the cathole is replaced. Owing to these and othertroul I18! and disadvantages, the pre- ,vious proposals were notpracticable and were ing the disadva stages heretofore encoimtered inthe oxygen sensitivity of such a nevernscd.

, It is among the objects of this invention to provide an apps rstus fordetermining oxygen concentration in :1 seous atmospheres. which makesuse of the princ lples of the rery cell while avoidattempting to \se itfor this pur ose. and which is simple. of pr: icticable sensitivity andaccuracy. is easily used, und is applicableto portable and ruggedapparai us adapted for high altitude and 0th "31:22am owing er '0 iappear from the foil description.

The inventio. i will be described with reference to the accompinyingdrawings in-which Fig-1 is a side eievai ion of the preferredembodiment. parts being broken away for clarity of illustration: Fig. 2a p lanview of the instrument shown in-I'lg. 1: Fig. 3 a verticalsectional view taken on line III-III. Fig. l; and Fig. 4 a wiringdiagram illustrative of one feature of the invention and embodied :n theinentshcwn in Pig. 1.

In accordance with this invention the objects are attained bymaintaining the current density at the cathode. or positive terminal, ofthe detector cell constant. In that manner the rate of hydrogen ii Inliberation per unit of area of the cathode is constant and thedepolarization E. M. F. produced by a given partial pressure of oxygenin the atmosphere being tested is likewise constant. By the applicationof my concept, therefore. it becomes possible to provide an insirumentwhich after being calibrated is of adeuate sensitivity for practicalpurposes and applicable to direct determination of oxygenconcentrations. and the determinations depend nei- (.hcr upon thecondition of the electrolyte or the anode, nor upon the temperature ortotal ressure as long as they are substantially uniform throughout thecell.

I apply this concept practically by restricting the area over which thegas comes into contact with the cathode-electrolyte interface. In otherwords. the cathode is so constructed or arranged in the cell that thetest gas exerts its depolarizin efiect over a predetermined area ofrestricted size. and can not come into contact with any other portion ofthe cathode-electrolyte interface.

I have found further that the higher the cathode current density is atthe start of the test.

or when the instrument is used with pure air. the

closer the calibration curve is to a straight line. Since the maximum E.M. F. available is of the order of 1.5 volts, the most practical way ofincreasing the current density is to restrict the active depolarizingsurface to a very small area. and if the area over which the test gas hmaccess to the cathode-electrolyte surface is sufficiently small, a closeapproach to a straight line calibration curve can be obtained.

The depolarizing electrode (cathode when considered interiorly, positiveterminal exterior-1y, of the cell) used in the practice of thisinvention is permeable by gases but is substantially impermeable by theelectrolyte with which it is used. For .most purposes I prefer to useporous carbon for this-purpose because of its negligible potential withespect to all electrolytes. However. electrodes possessing theproperties necessary for the purposes of the invention may be made fromother materials. including metals and alloys.

, The anode, or negative terminal. is a metal which is above thematerial of the cathode in the electrochemical series i. e., which forbrevity may sgidto bcelectroposltive to the cathode. Zinc +1Yb ,used asthe anode. but cadmium or other metals. clectropositive to the cathodecan be used if desired-for purposes of incieasing the life of the cellor for other reasons.

a condition of optimum and maintained uniformity. and the operating lifeof the cell is longer than where a llquid elcctrolyte is used. Moreover.there is the added advantage that the cells may be assembled and storedin a dry condition, the electrolyte being simply poured onto theabsorbent in the cell when it is to be put into use.

The apparatus provided by the invention comprises a primary cell whichincludes a container. or electrolyte chamber, in which there is disposeda body of absorbent material soaked with in solution of ammoniumchloride or other electrolyte. Mounted within the cell are twoelectrodes capable of generating an E. M. P. .when in contact with theelectrolyte. The electronegative electrode. suitably of carbon, is soconstructed and arranged as to have one surface in contact with theelectrolytc and the other surface available for contact with the gas tobe tested. and it presents only a restricted area in contact with theelectrolyte which is acted upon by gas which diffuses through theelectrode. The cathode in accordance with the invention, is soconstructed that gas can diffuse to the cathode-electrolyte interfaceonly through a restricted area of predetermined size, The electrodes areconnected electrically to a suitable meter or other means for In currentflow in the circuit thus established. together with adjustableresistance means for adjusting the current density at the cathode to apredetermined constant value.

In the use of the apparatus provided by this invention. the gas to betested is passed in contact with one surface of the cathode of a primarycell of the type Just described. in which depolarization can be effectedby oxygen from a gaseous atmosphere. the other surface of the cathodebeing in contact with an electrolyte of the type referred to above andwhich when current is drawn from the cell liberates at the cathodepolarizing ions, such as hydrogen ions, that are depolarized by oxygen.Initially air or other gas of known oxygen concentration is passed overthe cathode and the resistance of the circuit is adjusted to bring thecm'rcnt density at the active surface of the cathode to a predeterminedvalue. The standard gas is then replaced by the gas whose oxygen contentis to be determined and if its Althoughvarious electrolytes might beused. it i is at present preferred to use ammonium chloride. andcontrary to the customary practice in primary cell construction, Iprefer to use electrolytes of relatively dilute strength. Thereby thelife of thocell is increased by reason of less intense actionattheanode, and dimculties due to crystallization from the electrolyte arereduced. The exact concentration will depend. of course. upon theparticular salt used and such other factors as the sensitivity of theelectric meter. but generally speaking I prefer that the electrolyteshall contain not over about 5 per cent of solute.

It is important that the electrolyte of a portable instrument benon-spillable. I have found that this is accomplished satisfactorily bysoaking up the electrolyte in an absorbent material such as pumice orsponge. most suitably a fibrous absorbent such as absorbent cotton. Formost purposes I prefer to add to the absorbent material enoughelectrolyte so that it is almost but not quite saturated. This providesthe electrolyte in oxygen concentration is different than that of thestandard gas the degree of poiar'mation will be dliierent and willincrease or decrease the flow of current depending upon whether itsoxygen concentration. or partial'pressurc. is below or abovethatofthestandardgaaandthisresultwillbe measured by the meter in thecircuit.

The accompanying drawings represent the prcierrcd embodiment of theinvention and furthcr details and features of the invention will bedescribed with reference thereto.

1 The embodiment shown in Figs. 1 to 4 represents a portable apparatusmounted within a casing I provided with a removable cover plate 2 heldin position by screws 8. and for ease of assembly. use and repair all ofthe operative elements of the device are carried by this plate.

Extending through the cover late 2 is a tubular member 4 the upper endof which is provided with an outwardi! flanged portion between which andthe upper surface of the cover plate thsrcisdisposcdarcsilicntgashctt.For-ease of filling the electrolyte chamber with absorbent material itis preferred that the flanged portion be supplied as a member Iremovably connected totubuiarmemberlbyscrewthreads,asshown particularlyin 1'18. s. A base closure member I assoc scale iarthcst away item thestandardization point. Now in order to be able to adjust the instrumentto 21 per cent on air. the operator must turn switch II into position b.In this position or the switch, rheostat R-l introduces a higherresistance in shunt with meter ll than the one in position a; thus, nowwhen the meter pointer is adjusted to 21 per cent, a smaller current isdrawn Irom the detector cell than with the switch in position a. Sincethe decrease oi the current at 21 per cent against the original valuewith the small current loads used in this application is by larto thegreatest extent due to shrinkage of the active cathode area, rather thanto other causes, the observed decrease in current is a measure oi thisshrinkage. On this basis, the new value or the shunt to the meter iscalculated. It might appear at first sight that the series resistance inrheostat 3-4, when changing from switch position a to 1:, could be leftconstant or decreased. However, a closer mathematical investigation aswell as experiments .have shown that (except it the outside resistanceswere to be made imprsctically small in comparison with the cellresistance) in order to obtain constant current density the seriesresistances in Ft-l must also be when the shunt resistancu lt-l areincreased. Formulae to calculate the nest resistances in R-I.corresponding to dinerent values oi R-i have been worked out. Theirvalidity has been checked by experiments using a second known oxygenconcentration.- This experimental method may also be used by thoseskilled in the art to find without calculation the proper resistancevalues needed to keep the calibration curve constant. By way of anexample, in one instrument that had a substantially constant"calibration throughout its liie, shunt resistances in R-l were inpositions 0-60 ohms, b-lOO ohms, o-300 ohms, d-inflnity. Thecorresponding series resistances for constant current density andconstant calibrations were: 0-200 ohms, H50 ohms, 0-560 ohms, d-750ohms. The meter-.us'e'd had a resistance 01.75 ohms and a scale range of150 microamperes. Rheostat R-4hadaran eori50ohma' The meter scale usedwith the apparatus pro vided by the invention can be calibrated readilyby the use of a series oi gases or known ongen concentration between thelimits {or which the apparatus is to be used. I'br instance. it theinstrument is to be used (or measuring oxygen deficiency 0! airatmospheres pure air my be used to the the upper limit (21% 0:) o! thescale, and the meter deflection for lower concentrations can bedetermined by using a series of gases. such as nitrogen-oxygen mixturescontaining less than 21 per cent at oxygen. By restriction oithe activearea of the cathode to produce a high cathode current density,.inaccordance with ,the principles of th.is"invention,, there will beobtaineda calibration curvecxempliiled' by theiollowing data obtainedwith one instrument construe ted asdescribed above:

Misre- Oxymperemt ammetor 3 hi I 1 %a DJ 46.. ii... .31,

' invention. have.

The ioregoing calibration data apply to the case where the cathodecurrent density at 21 per cent oxygen is about microampcres per squaremillimeter.

In the use of the apparatus of this invention the first step is toadjust the cathode current density to that of the reference standardwhich in the case of oxygen deficiency meters will be that correspondingto 21 per cent oi oxygen. That is. the current density will be adjustedto cause a meter deflection against pure air the same as was obtained incalibrating the instrument. To thisendtheswitchllisclosedandordinary airis passed through the cathode by means 0! aspirator bulb H, which drawsair in from the atmosphere and forces it through scrubber ll whence itpasses through side arm II and tube is into the bore "a oi cathode II.The e!- iiuent air then escapes to the atmosphere throughtheiateralcpeningincaplt. RheostatR-Sis adjusted until the pointer oimeter 23 indicates 21 per cent oi oxygen. At this point the cathodecurrent density has been adjusted to the predetermined constant valueand the instrument is ready for use with the gas which is to be tested.The latter gas is then passed through the instrument by aspirator bulbl1, and the diflerence in depolarizat on due to the diflerence in oxygencontent will aii'ect the flow of current in the circuit and will beindicated by the meter reading.

Utheinstrumcntisusediormakingaseries oi omervations it will ordinarilysui'iice to check the standard setting only occasionally. sat atintcrvals o! afew hours. Onthe otherhand. i! the instrument is usedinfrequently the current density should be adjusted each time it isused, butthisisdonecasilyandquicklymerelybypassingairthroughitinthemannerdescribed.For ease of checking or adjusting. to the standard current density inatmospheres where air is not readily available. a small bottle oistandard gas under pressure may be'provided which is connected to aconduit I" which brpesses scrubber leandisconnecteddirectlytotube,asshown in Figs. '1 and 8.

, Various modifications are, of course. permissible. For-instance,instead oi the electrical circuit described above there may be usedother means for accomplishing the same mult, as by replacing the coupledrheostats R-l and 3-! by a pairoitandemrheostatsotthetypeusedinredlocircuits. Or. a radio type rhcostat together with a step-by-steprhcostat may be used, the Iormer having a dial marked in correspondencewith the successive steps of the latter. Other modifications-oi acircuit (or keeping the current densityconstantwilloccur-tothoseskitledintheart. Likewise. the tubular. cathodemight be replaced by a-porom'cathode mounted in the wall oithe cellwith: its inner surface in contact with =thc and with the gas passedover its" cuter m the embodiment shown. rheostatlt-lisaridiotnesliderrheostatwhichincorpotato: switch a of Hg. 4.

Thisapplicationisadivisionormycopendlng application Berial l'lo.488.046. iiled May 22, 1943, new Patent No. 3.464.987 dated larch s,1249.

According to the provisions of patent l etutes. I have explained theprinciple, preierrcdembodimentandmodeot operation of my what Inowconlider to represent its best embodiment However, I desireto have itunderstood that. withintheseopeettheappended claims.

the invention may be practiced otherwise than as specificallyillustrated and described.

I claim:

1. Apparatus ior measuring oxygen deficiency of air atmospherescomprising a container, absorbent material disposed in said containerand soaked with a dilute solution of ammonium chloride, a tubular porouscarbon electrode acting as a cathode disposed with only its outersurface in contact with said electrolyte, a zinc anode disposed incontact .with said electrolyte, said cathode having only a small areaits electrolyte contacting surface relative to the surface of the anodeelectrically conductive, an electric circuit including the cell iormedby said container, electrodes and electrolyte, together with means iormeasuring current how in the circuit, and adlustable resistance meansfor adjusting the current density at the conductive portion of saidcathode; and connections to the bore of said cathode tor flowing airtherethrough out of contact with the electrolyte.

2. Apparatus for measuring the concentration oi oxygen in gasescomprising a container. a pair of primary cell electrodes disposed insaid con tainer. an'electrolyte contained in the container in contactwith said electrodes and productive oi hydrogen polarization at one oisaid electrodes. the polarizable electrode being permeable by gas butnot by electrolyte and having exposed to said electrolyte anelectrically conductive suriace that is small relative to theelectrically conductive area of the other electrode, to thereby providehigh current density and concentration 01 polarizing material thereat.means Xor passing gas to be tested over a surface or said poiarinableelectrode that is not in contact with said electrolyte, an electriccircuit comprising said electrodes and electrolyte, means tor measuringelectric current in thecircuit; and adjustable resistance means foradjusting the current density at said pciarizabie electrode to apredetermined constant value and comprising a continuously variablerheostat in series with the cell andmeasuringmeanaandapairoisimilarcoupledstepby-step rheostats one of whichis in series with said continuously variable rheostat and the other orwhich is in shunt with said measuring means, said coupled rheostatsbeing constructed to ini0 troduce pmgressiiely inereasins resistances inseries with said nriahle rheostst and in shunt receiving electroly te,an anode container for coal act with the electrolyte, bular cathodeelutronegative to said anode posed in the container. connections 1 thebore of said cathode. said its cute: surthe gas through an! mesons crrnnThe following :eierenca are of record in the die oithis patent:

UNITE) STATE PATENTS Nmnber Name Date 1,901,344 Baton Mai. 14, 19332,156,693 Jacobson May as, 1939 2.810371 Harts liar. 0. 1m 2.401.287Tacit et al. his! 88. 1946 ED233108 PATENTS Number Country Date $25,423On :at Britain Aug. 28. 1940 668.080 Ge rsnany Aug. I, 1938 OTIKERWCEBSer. No. 282.291 tasarhenkei (LP. 0.). published Bay 11. 1948.

"transactions or the Ilectrochemiml Society.voLsfllwhplselwthroughmmubiicstionbynerientitled'nneveraibleoxygenllectrode." mma'ladustrie Chimique."vol. 30. (use). paces

